Sucrose is a sugar. The concentration of a solution of sucrose can be measured by the optical rotation, α, of a sucrose solution. The more concentrated the solution, the greater the optical rotation of the solution. A polarimeter is used to measure optical rotation. Light is passed through a sample of the sucrose solution in a glass cell, and the observed angle of rotation, αobs, is measured. A simplified diagram of a polarimeter is shown. [Figure X.X] If a glass cell of length 10 cm is filled with a solution of sucrose of concentration 1 g cm⁻³ the measured angle of rotation is known as the specific rotation, [α]. The observed angle of rotation, αobs, measured by the polarimeter is related mathematically to the concentration of the sucrose solution by the equation shown. αobs = [α]c αobs is the observed angle of rotation using a 10 cm cell [α] is the specific rotation of sucrose solution c is the concentration of sucrose, in g cm⁻³ A student wanted to determine the specific rotation of sucrose, [α]. Solutions of different concentrations of sucrose at 20 °C were placed in a polarimeter and the observed angle of rotation, αobs, recorded. The '+' sign is used to show that the rotation is in a clockwise direction.